The present invention relates to a method for the inhibition of corrosion in particulate zinc, especially for use in rechargeable zinc-air batteries generally, and more particularly, in such batteries intended for use in electric vehicles and energy storage systems.
Various proposals have been made in the past for electric powered vehicles. To date, for a number of reasons, electric vehicle systems have yet to become commercially viable generally, for urban and highway applications. There have been proposals to employ zinc/air batteries for urban vehicle propulsion. An example is the following publication: Improved slurry zinc/air systems as batteries for urban vehicle propulsion, by P. C. Foller, Journal of Applied Electrochemistry 16 (1986), 527-543.
Metal/air battery structures are described in the following publications: U.S. Pat. No. 4,842,963, entitled Zinc Electrode and Rechargeable Zinc-Air Battery; U.S. Pat. No. 4,147,839, entitled Electrochemical Cell with Stirred Slurry; U.S. Pat. No. 4,908,281, entitled Metal/air Battery with Recirculating Electrolyte; U.S. Pat. No. 3,847,671, entitled Hydraulically-Refuelable Metal-Gas Depolarized Battery System; U.S. Pat. No. 4,925,744, entitled Primary Aluminum-Air Battery; U.S. Pat. No. 3,716,413, entitled Rechargeable Electrochemical Power Supply; U.S. Pat. No. 4,925,744, entitled Primary Aluminum-Air Battery. In U.S. Pat. No. 3,592,698, entitled Metal Fuel Battery with Fuel Suspended in Electrolyte, there is described inter alia a method for circulating an electrolyte/metal fuel powder mixture through the batteries; U.S. Pat. No. 4,126,733, entitled Electrochemical Generator Comprising an Electrode in the Form of a Suspension, relates to a similar subject using a circulated suspension of inert cores coated with an electrochemically active material. In U.S. Pat. No. 4,341,847, entitled "Electrochemical Zinc-Oxygen Cell", there is described a method in which an electrolyte is circulated in the annular space between concentric electrodes.
Electrical energy storage systems are described in the following publications: U.S. Pat. No. 4,843,251 entitled Energy Storage and Supply Recirculating Electrolyte; Energy on Call by John A. Casazza et al, IEEE Spectrum June, 1976, pp 44-47; U.S. Pat. No. 4,275,310, entitled Peak Power Generation; U.S. Pat. No. 4,124,805, entitled Pollution-Free Power Generating and Peak Power Load Shaving System; U.S. Pat. No. 4,797,566, entitled Energy Storing Apparatus.
Regeneration of spent zinc-containing alkaline electrolyte is described in a number of prior patents. For example, in U.S. Pat. No. 3,847,671 (mentioned above) whole spent electrolyte is subjected to electrolysis, when zinc deposited at the cathode is removed with a wiper blade. The thus-removed zinc is said to be substantially heavier than the electrolyte (35-40% KOH) and thus falls to the bottom of each cell. In a particular embodiment, the cathode and anode are specified as being made from copper (or silver-plated copper) and carbon, respectively. In U.S. Pat. No. 3,981,747, it is proposed to regenerate the spent zinc in an alkaline electrolyte by reaction with a strongly electronegative metal, such as magnesium or aluminum, which displaces the zinc. In U.S. Pat. No. 4,341,847 (also mentioned above), spent zinc in the alkaline electrolyte is regenerated either by reversing the current and plating zinc on the anode, or by merely mechanically replacing zinc oxide particles by active zinc particles.
It is of importance in batteries containing zinc electrodes that the zinc should not be consumed by a reaction with aqueous electrolyte, especially alkaline electrolyte, which generates hydrogen gas, which reaction merely corrodes the zinc and prevents its availability of the latter for producing electric current. A number of prior patents relate to this problem. Thus, e.g., in U.S. Pat. No. 4,112,205, double salts containing both mercuric and quaternary ammonium ions, are used as inhibitors in galvanic cells comprising zinc anodes, notably in Leclanche type batteries containing ammonium chloride/zinc chloride electrolyte; U.S. Pat. No. 3,945,849 employs quaternary ammonium halides as inhibitor for zinc anodes in similar primary cells. U.S. Pat. No. 4,195,120 teaches alkaline cells containing a predominantly zinc anode and as a hydrogen evolution inhibitor, a surfactant which is an organic phosphate ester of the ethylene oxide adduct type. Metal oxide inhibitors for zinc (in practice ZnO) electrodes are described in U.S. Pat. No. 4,084,047, in which the inhibitors are mixed thoroughly into the ZnO; the inhibitors taught in this patent are binary combinations of oxides which exclude mercuric oxide, the latter being regarded as an unsatisfactory additive for the ZnO electrode. According to U.S. Pat. No. 4,084,047, it was known to mix or alloy the active zinc in zinc-zinc oxide anodes and its supporting grid (e.g. copper or silver structures) with 0.5-5.0 wt. % mercury or mercuric oxide). It will also be appreciated by persons skilled in the art that amalgamation of zinc with mercury has been known for a very long time and that it is carried out in neutral, or more usually in acid solution, e.g. by reacting zinc with mercuric chloride in dilute hydrochloric acid.
The disclosures of all of the foregoing publications (including patents), including also the prior art described therein, are explicitly incorporated herein by reference.